The present invention relates to nuclear power reactor fuel bundles. More particularly, it discloses a novel and improved method and apparatus for assembling a fuel bundle for use with such nuclear power reactors.
The production of power from nuclear fission may be accomplished in several ways. A commonly used commercial apparatus uses a boiling water reactor. In such reactors, the heat generated by nuclear fission is removed by the boiling of water. The steam produced is sent to a turbine which drives an elecrical generator. After passing through the turbine and thereafter being condensed, the water is recycled to the reactor where it is boiled again. While such a cycle is analogous to conventional steam boiler plants in its broadest aspects, there are many problems unique to the operation in which heat is supplied by nuclear fission.
In boiling water reactors, the fission occurs within so-called fuel rods which are assembled into bundles, a multiplicity of which are located in the fuel core of the reactor. Water surrounds each bundle and passes upward between the fuel rods as heat is received from the nuclear fission reaction.
As the reactor operates, the fuel is gradually consumed and it is necessary at periodic intervals to replace the fuel by replacing the fuel bundles. In order to operate the reactor under optimum conditions, usually only a fraction of the fuel bundles are replaced at any one time. If there is a failure of the bundles which permits radioactive materials to enter the water stream the fuel bundles must be repaired. Because of the presence of radioactivity these bundles must be disassembled and repaired by remote control. Thus the fuel bundles should be as mechanically simple as possible an be readily adaptable for remote disassembly.
In the prior art as typified by U.S. Pat. No. 3,431,170 it has been common for fuel bundles to be assembled from groups of fuel rods spaced and suspended between end plates which act to fix the fuel rods in position relative to each other. In order to minimize expansion difficulties under the high temperatures at which the nuclear reaction occurs and at the same time to minimize the disassembly problem, fuel rods commonly float between the end plates. The rods have a projection at one end which fits into a corresponding hole in one end plate. There is a similar arrangement at the other end plate with the exception that around the rod there is placed a spring which is compressed when the bundle is assembled. Tie rods are employed to hold the assembled end plates together. These tie rods have commonly been threaded at one end so as to be securely fastened into the first end plate. The other end of the tie rod passes through an opening in the second end plate and is secured by a nut bearing on the second end plate. Locking devices such as discussed in the above-referenced patent have been used to prevent the nuts from loosening in service. As will be appreciated, the use of a nut and bolt inherently complicates the disassembling process. Therefore, it is an object of the present invention to provide an alternate means for assembling nuclear fuel bundles which does not involve the use of nuts and bolts and simplifies disassmbly by remote control.
Other objects of the invention will be made evident within the descriptin of the invention which follows: